1. Field of the Invention
The present invention relates to an alumina porous material and method of producing the same and in further detail, to an alumina porous material that shows a balance between porosity and specific surface area and mechanical strength and that comprises many micropores, has a high specific surface area and is high strength such that it is ideal when used for filters, catalyst carriers, etc. Additionally, the present invention relates to an alumina porous material having high strength and a method of producing thereof.
2. Description of the Related Art
Ceramic porous materials have excellent heat resistance, thermal shock resistance, chemical resistance, normal-temperature and high-temperature strength, light weight, etc., and have been an indispensable industrial material in the past in the form of various filters (gas separation, solid separation, bacteria elimination, dust elimination, etc.), catalyst carriers, acoustic materials, insulating materials, sensors, etc.
Nevertheless, there has recently been a demand for higher porosity, higher strength, and better heat resistance when used in filters and catalyst carriers, etc., and fulfilling this demand is proving difficult with conventional ceramic porous materials. The alumina porous materials that are used for various filters and catalyst carriers are mainly xcex3-alumina, but there is a problem in that xcex3-alumina goes through phase transition to the stable xcex1-alumina phase at approximately 1,000xc2x0 C., resulting in a marked drop in specific surface area and loss of its function as a catalyst carrier.
Therefore, there is a desire for the development of catalyst carriers with such excellent heat resistance that a high relative surface area can be expected, even at high temperature. Incidentally, it is already known that the temperature of conversion from xcex3-alumina to xcex1-alumina changes markedly with the addition of oxide, etc., to xcex3-alumina, and in particular, there is a marked rise in the transition temperature and the high relative surface area of xcex3-alumina can be retained at a high temperature by adding silica to xcex3-alumina, as reported in xe2x80x9cThermal stabilization of an active alumina and effect of dopants on the surface area (B. E. Yoldas, Journal of Materials Science, 11, 465-470 (1976) ).
A variety of methods of producing alumina porous materials have been studied. Porosity and mechanical strength are affected by the sintering conditions of the sintering method. There is usually a dramatic drop in porosity of alumina with an increase in the sintering temperature. Therefore, sintering must be incomplete in order to retain porosity. However, it is difficult to control porosity, or mechanical strength decreases markedly making practical use difficult, with sintered compacts produced by these incomplete sintering methods.
As previously explained, attempts are being made to produce alumina porous materials by conventional incomplete sintering methods while adjusting the starting material composition, sintering conditions, etc., but it is difficult to balance porosity and specific surface area with mechanical strength. In particular, an alumina porous material having uniform pore diameter and high porosity and specific surface together with excellent mechanical properties is necessary when it is used as a filter or catalyst carrier.
Under such conditions, the inventors repeated intense research aimed at developing an alumina porous material having high porosity and high specific surface area and excellent mechanical properties in light of the above-mentioned conventional technology and discovered that the desired goal can be accomplished by using a structure wherein using a mixed powder of aluminum hydroxide mixed with alumina as the starting material, this mixture is heated to decompose the aluminum hydroxide and the product is further calcinated at a high temperature. They successfully completed the present invention as a result of further research.
The object of the present invention is to provide an alumina porous material with which pore diameter is controlled, porosity and specific surface area are high, and mechanical strength is excellent and to provide a method of producing thereof. This invention relates to a method of producing an alumina porous material using a mixed powder of alumina powder and aluminum hydroxide represented by the chemical formula Al(OH)3 at different percentages as the starting material, comprising the steps of heating this mixed powder to decompose the aluminum hydroxide and further heat treating it within a temperature range of 1,000 to 1,600xc2x0 C., and to the alumina porous material produced by the above-mentioned method with a porosity exceeding 40 volume % and its specific surface area of 8 to 40 m2/g, and further to a filter and catalyst carrier that are obtained using this alumina porous material.
The purpose of the present invention is to provide an alumina ceramic porous material having excellent mechanical strength while also having a sufficiently narrow pore diameter distribution and retaining high porosity and high specific surface area, as well as a method of producing the same and the use of the same.
The present invention for solving the above-mentioned subject comprises the following technical means:
(1) A method of producing an alumina porous material using a mixed powder of alumina powder and aluminum hydroxide represented by the chemical formula Al(OH)3 at different percentages as the starting powder, comprising the steps of:
heating the molded article of the same starting powder to decompose the aluminum hydroxide and
further calcinating it at a temperature of 1,000 to 1,600xc2x0 C.
(2) The method of producing an ceramic porous material according to (1) above, wherein the material contains 1 to 20 volume % aluminum hydroxide and, when necessary, zirconia, as its ceramic components other than alumina, which is the main component.
(3) The alumina porous material,
said material is produced by the method defined in (1) or (2) above, and its porosity exceeds 40 volume % and its relative surface area is 8 to 40 m2/g.
(4) The alumina porous material according to (3) above, wherein the material has a pores structure having at least one pore distribution peak within the range of 10 to 1,000 nm.
(5) The ceramic porous material according to (3) or (4) above, wherein the alumina phase composition is xcex1 and xcex8 and the ceramic porous material has high porosity, high relative surface area and high strength as a result of controlling xcex8xe2x80x94xcex1 phase transition by adding a second phase.
(6) A filter, which is obtained using an alumina porous sintered material obtained by the production method in (1) or (2) above.
(7) A catalyst carrier, which is obtained using an alumina porous sintered material obtained by the production method in (1) or (2) above.